직접에너지적층 공정으로 제조된 다공성 알루미늄의 적층 특성과 기계적 특성에 관한 연구

Abstract

This study focuses on the manufacturing of porous materials using the directed energy deposition (DED) process which is one of the 3D printing techniques. A deposited aluminum foam was manufactured by mixing AlSi10Mg and a foaming agent ZrH2. The foaming properties, microstructure, compression behavior, and wear properties were comparatively analysed. As a result of the experiment, the foaming agent forms pores inside the deposited material through a chemical reaction; and the intermetallic compound Al3Zr is generated through a reaction with aluminum powder. It was confirmed that Kirkendall void was created by diffusion of Al3Zr along with pore generation according to the foaming agent. In addition, when a high content of ZrH2 is used, the thickness of the oxide film increases, resulting in defects at the interface. Meanwhile, the effect on the porosity, the number of pores, the size of the pores, and the deposition height according to laser power, which are representative process variables, was analyzed. As a result, a aluminum foam with a maximum porosity of 28.73% at a laser power of 1100 W could be manufactured. During deposition, it contributes to stabilization of foam by forming oxides by metal elements contained in the alloy. When ZrH2 is alloyed with aluminum, the protective properties of the oxide film increase, which affects the oxidation activity. Therefore, it was found that the porosity and pore size were high because relatively many oxides stabilized the pore growth. The Zr particles inside the deposited region show high hardness because they are embrittled by hydrogen, nitrogen, and oxygen. As a result, even though pores were generated inside the deposited material, the hardness of the foam-deposited material did not decrease compared to the non-porous material. The compression test of non-porous and porous materials showed that the porous structure made by the pores generated therein collapses to absorb compression energy and become more dense as the internal pores are removed. Therefore, the specific energy absorption rate, which is an advantage of foaming materials, was high. Due to porosity, the yield stress decreased, but the elastic modulus increased by the residual particles. The Al/Zr system was highly wet and the intermetallic compounds were uniformly dispersed. As a result the wear test, the amount of weight loss is smaller than that of non-porous materials as wear debris accumulates and compresses in the pores.